The criminal complaint was lodged with a federal court in the Eastern District of Virginia, court documents show, and a provisional arrest warrant had been issued, officials said.

On Saturday a senior US administration official said: "If Hong Kong doesn't act soon, it will complicate our bilateral relations and raise questions about Hong Kong's commitment to the rule of law."

Beijing influence

Mr Snowden left a hotel in Hong Kong on 10 June after allowing newspapers to name him as the source of the leaks.

His current whereabouts are unknown. However, a report in Hong Kong's Sunday Morning Post suggested he was "in a safe place" in the city and not in custody, nor under police protection, as reported elsewhere.

Hong Kong, a Special Administrative Region of China, signed an extradition treaty with the US in 1998.

It has a separate legal system from the Chinese mainland, and Mr Snowden's right of appeal could drag out any future extradition proceedings for several years.

Some Hong Kong politicians have voiced support for Mr Snowden.

Left-wing MP Leung Kwok-hung said Beijing should tell the authorities to protect him from extradition, and the people of the territory should "take to the streets" to shelter him.

The BBC's Juliana Liu in Hong Kong says Beijing is highly unlikely to interfere in the early stages of what could be a long legal battle.

The leaks have led to revelations that the US is systematically seizing vast amounts of phone and web data under an NSA programme known as Prism.

Mr Snowden also alleged that US intelligence had been hacking into Chinese computer networks.

Further details of his allegations emerged on Sunday in a report by the Sunday Morning Post, which said that as recently as January this year the NSA hacked computers and servers at the prestigious Tsinghua University in Beijing.

He said earlier that he had decided to speak out after observing "a continuing litany of lies" from senior officials to Congress.

US officials have since defended the practice of gathering telephone and internet data from private users around the world.

They say Prism cannot be used to intentionally target any Americans or anyone in the US, and that it is supervised by judges.

'Treasonous act'

Mr Snowden is charged with theft of government property, unauthorised communication of national defence information and wilful communication of classified communications intelligence.

Each of the charges carries a maximum 10-year prison sentence. The complaint is dated 14 June although it was made public only on Friday.

In the US, the charges were welcomed by Democratic Senator Bill Nelson, a member of the Senate Armed Services Committee.

"I've always thought this was a treasonous act,'' he said in a statement. "I hope Hong Kong's government will take him into custody and extradite him to the US."

"The US government is spying on each and every one of us, but it is Edward Snowden who is charged with espionage for tipping us off," said Mr Assange, who has been living in Ecuador's London embassy for the past year, fighting extradition to Sweden for questioning on alleged sex offences.